1. Field of the Invention
The present invention is broadly concerned with a modular waste treatment apparatus of the type designed to be placed, either singly or in parallel relationship with other modules, in a waste treatment basin in order to provide the primary functions of aeration and sedimentation as a part of an activated sludge system. More particularly, it is concerned with such a module which efficiently performs the function of aeration, flocculation, sedimentation, sludge return, effluent collection and skimming, all with a minimum of utility and overhead expense. Particular features of the module include a novel waste inlet/flocculation compartment which promotes a agglomeration of solid waste particles as an aid to sedimentation within the module; and a collection/solids withdrawal apparatus serving to uniformly pump collected solids upwardly for return to the basin.
2. Description of the Prior Art
Newly developed housing communities or mobile home parks often are not connected with large, existing municipal sewage treatment systems. As a consequence, builders of these communities are often required to provide a sewage treatment facility as a part of the overall development plan. It has been known in the past to construct concrete sewage collection basins for these purposes, and to install one or more modular treatment units within the basin to handle the sewage load. For example, U.S. Pat. No. 3,975,276 describes such a modular device which has achieved widespread use.
Generally speaking, treatment of solids-containing liquid waste in modular basin systems involves aerating the wastewater so that bacteria will grow that consume the pollutants therein, thereby inducing further bacterial growth. Eventually, a flocculent suspension is created (often referred to in the art as "mixed liquor"), and if this suspension is settled out a clear supernatant, with the pollutants removed, may be withdrawn for direct discharge into natural receiving bodies of water. The settled suspension remains in the basin, however, so that the bacterial suspension can continue to consume wastewater pollutants. This suspension must not be allowed to sit quiescent for an extended period within the basin, or it will start to self-decompose, releasing gasses into the settled sludge mass. This in turn will cause the sludge to lighten and float to the surface, where it will contaminate the otherwise clean water supernatant that is to be discharged.
Accordingly, in order to render the activated sludge process efficient, the settled sludge suspension must be uniformly handled, mixed and returned to the basin so as to inhibit self-decomposition thereof. At the same time however, the handling of wastewater solids must not create undue currents which interfere with the necessary settling and pollutant consumption. This is a distinct problem with many prior art clarifiers, which actually create sizeable currents by virtue of the manner in which the suspension is introduced into the clarifier. Prior expedients used to convey the suspension into clarifiers involve pipes, slots and baffles of many different designs which attempt to prevent and reduce undue entrance currents.
Prior workers have understood that settling or flocculation of solids within a quiescent zone can best occur when the solid particles have first been introduced into a zone of gentle mixing where the particles may agglomerate or flocculate into larger sizes. If then directed into a quiescent area, they will settle faster and much more effectively. While this settling mechanism has been appreciated, little has been done to effectively implement it. Normally, this would require a separate flocculation basin between an aeration tank and a sedimentation tank, through which the waste would flow. To keep solids from settling out within this flocculation basin, and to provide gentle agitation to promote flocculation, it would be necessary to add mechanical mixing devices, which in turn adds both capital and operating expense to the system. Because of these difficulties, most conventional clarifier designs directly introduce agitated suspension without an intermediate flocculation stage. This has correspondingly detracted from the efficiency of prior clarifier designs.